Forming equipment having first and second opposed series of mold blocks for forming a moving mold tunnel are well known and used in association with plastic extruders for forming elongate plastic products including tubing, and corrugated plastic pipe. A first series of mold blocks co-operate with an opposed second series of mold blocks to form a moving mold tunnel. The mold blocks effectively circulate between an entrance where the mold blocks engage to form the mold tunnel and an exit of the mold tunnel where the mold blocks separate and are recirculated to the entrance. The first and second series of mold blocks typically circulate as side by side mold blocks or as upper and lower mold blocks.
This type of forming arrangement can be used for extruding pipe and other elongate structures and has particular application for extruding corrugated pipe and double walled corrugated pipe having an inner smooth wall and an outer corrugated wall secured thereto. Other cross sectional shapes can be used and are known.
The demand for both small and large diameter corrugated pipe continues to increase and the speed of manufacture has also increased. Corrugators can now operate at speeds in excess of fifty meters per minute. This increase in speed typically requires a longer mold tunnel and a corresponding increase in the number of mold blocks.
Typically in pipe corrugators, the moving mold blocks are pushed at one end by a drive arrangement for movement along a guide track and it is this drive arrangement that continues to push the mold blocks back to the drive arrangement. On the return path at the drive arrangement there is a thermal expansion gap defined between the lead mold block just engaged by the drive arrangement and the following mold block being pushed to the drive arrangement. This thermal expansion gap separates the mold blocks and allows for thermal expansion of the mold blocks caused by the operating temperature of the mold blocks. The amount of thermal expansion is also a function of the cooling efficiency of the one or more cooling arrangements associated with each of the series of mold blocks.
The present invention will be described with respect to a first series of mold blocks and an associated lower second series of mold blocks (vertical layout), however it can be appreciated that this type of equipment can be of a horizontal or other angular layout of opposed series of mold blocks.